1. Field of the Invention
The invention relates to a sheet supplying apparatus for separating and conveying a plurality of sheets placed thereon one by one.
2. Description of Related Art
As a sheet reading apparatus for use in an image processing apparatus such as a scanner apparatus or a copying machine, there is known one using two reading methods together. One of the methods is a fixed-reading method of scanning an original in a fixed state by a scanner, and reading the image of the original. The other is a flow reading method of reading the image of an original while conveying the original with the scanner fixed.
In recent years, color image forming apparatuses have spread and in an automatic original supplying (feeding) apparatus carried on the above-mentioned sheet reading apparatus, opportunities for supplying color originals have increased. Particularly, in color printing of high resolutions, importance is attached to the quality of image and therefore, it has been necessary to read a color original in a stable state. In the aforedescribed flow reading method, the image of an original is read while the original is conveyed and therefore, the vibration of the original itself being conveyed, or a blurred image due to the shock at a moment when the leading edge of the original cuts in between rollers in the automatic sheet feeding apparatus or the trailing edge of the original leaves the rollers has occurred, and various problems have arisen in realizing color printing of high resolution.
Also, due to the difference in quality of paper between a color-copied sheet used as an original (hereinafter referred to as the color original) and a black-and-white original, for example, the difference in the thickness (μ) of paper or the applied amount of oil or the like, even if the automatic sheet feeding apparatus is caused to effect the same control for originals differing in quality of paper from each other, it has been impossible to realize a similar operation. Particularly, when the applied amount of oil is great, it has been difficult to separate originals placed on an original tray one by one.
As what controls such an original supplying operation, there is known an automatic sheet feeding apparatus which is designed such that a movement speed V1 when separating and conveying originals having image information on one side only thereof and a movement speed V2 when separating and conveying originals having image information on two sides thereof assume the relation that V1>V2, and which is improved in separating performance and can prevent a plurality of originals from being paid away at a time (for example, Japanese Patent Application Laid-Open No. 2001-130769).
Also, there is known an automatic sheet feeding apparatus which, before main scan, judges an original to be color-reproduced or an original to be black-and-white-reproduced after the original has been conveyed onto an original plate (platen glass) (for example, Japanese Patent Application Laid-Open No. 2002-281322). Also, there is known an automatic sheet feeding apparatus which discriminates whether an original is monochromatic or polychromatic, and changes a reading speed to a low speed mode when the original is discriminated as polychromatic (for example, Japanese Patent Application Laid-Open No. H10-42158).
The above-described conventional sheet reading apparatus, however, has suffered from the following problem and a solution thereto has been desired. That is, before the originals are separated and conveyed, it has been impossible to obtain information regarding the originals placed on the stacking tray. Therefore, when for example, originals are to be separated and conveyed one by one from a bundle of originals comprising a mixture of color originals and black-and-white originals, it has been impossible to perform the optimum separation and conveyance (supplying operation) of the sheets unless a user changes setting each time.